The invention generally relates to digital filters, and relates in particular to linear-phase finite impulse response (FIR) low pass filters for filtering digital data.
Digital filters may be used to reduce the amount of digital data to be transmitted, stored or processed in a digital signal processing system. In various applications, unfiltered data may be too voluminous to be transmitted, stored or processed, and in some applications, unfiltered data may even include unreliable or unwanted data that should be removed. The removal of certain of the digital data, however, presents the challenge that the desired information generally contained in the data should not be lost in the process.
Digital filters may remove or ignore data from a data input stream that is rapidly changing. For example, if input data may range from 100 to −100 at an input rate of x samples per second, then the fastest input changes would be a sequence of 100, −100, 100, −100 etc. for sequential bits. This may be considered a high frequency input stream and a digital filter may be used to remove the high frequency component of the input stream permitting less rapid changes in the data to pass through the filter.
For example, U.S. Pat. No. 6,668,013 discloses a digital filter that employs multipliers, but the use of a many multipliers in circuits typically adds considerable complexity and cost.
There continues to be a need, therefore, for an efficient and economical linear-phase FIR low pass filter for filtering digital data.